Communication system



1945. R. H. HERRlcK 2,383,312

COMMUNICATION SYSTEM Filed July 21, 1943 -9 Sheets-Sheet l CONTROL EQUIPMENT I38 Yes meg 1 Ffi j OPERATOR NUQ \f' V F PERIODIC I2 LINE r126 TROUBLE AMF. FAILURE n5 us ae 54 -l53 lsl lsz JNVENTOR. -RO$WELL H. HERRICK! 7 BY 1 lOaazmfind/a wm A ORNE S R. H. HERRICK 2,383,312

COMMUNICATION SYSTEM Filed July 21, 1943 'Aug. -21,' 1945.

9 Sheets-Sheet '7 mvuron ROSWELLH; HERRICK ATTORNEYS All 2i, 1945. v

R. H. HERRICK COMMUNICATION SYSTEM Filed July 21, 1943 9 Sheeflsl-Sheet 8 POWER SUPPY COMMERCIAL a AUXILIARY SOURCES SPARE TIMER BIG INVENTOR ROSWELL H. HERRICK BY Am,v6l -,M18m

ATTORNEYS 1945. R. H. HERRICK 2,383Q312 COMMUNICATION SYS TEM Filed July 21, 1943 I 9 Sheets-Sheet 9 ROSWELL H. HERRICK I BY .oww,f- ,md%n

ATTORNEYS Patented Aug. 21, 1945 s PATENT FICE COMMUNICATION SYSTEM Roswell H: Herrick, bak Park, Ill., assignor to I V I Automatic Electric Laboratories, Inc., Chicago,

. I I Ill., a corporation of Delaware h Application July 21, 1943, Serial No. 495,548 35 Claims. (Cl. 1 79-5) @This invention relates to communication systerns, and, more particularly, to communication systems of the type suitable for use by fire or I police departments. h l

Fire andpolice departments require communicationsystems which have as a prime characteristic service reliability together with certain desired features, 'such as simple and rapid communicationbetween a control station and any one ,of a plurality. of selected outlying stations. I In order to provide the service. reliability, certain spare or duplicate equipmentparts are provided at the control station, and at both the control station. and the outlying sations emergency power supplies are provided. Preferably the shift from one set of. equipment to. the spare or duplicate equipment is brought about automatically together with a notification to the attendants of i such change. i Each emergency switching opera tionis'preferably automatic, and associated faciliti es are provided which require acknowledgement by the attendants to insure proper, attention, thus guarding against neglect to correct the abnormal conditions. In order that the telephone linesbetween the control station and the outlying stations provide reliable service, itn is desirable to provide continuous line-short and lineopen tests together with frequent periodic ground tests for eachline, together with suitable signals audible or visual or both, which must be acknowledged by the attendants.

In providing communication betweenthe conconnection between the control station amplifier and one or more of lines.- V h p It, therefore, is an object of the present invention to provide animproved communication the outlying station telephone system between a control station and a plurality of outlying stations, wherein reliable. operation is provided by providing continuous tests for open-circuit. and short-circuit conditions on the telephon lines.

object of the present invention to v It is another provide an improved communication system wherein each conductor of the various telephone lines interconnecting the control station with a plurality of outlying stations is periodically tested for ground. I

It is another object of the present invention to provideperioclic testsof the operativeness of the loudspeakingcommunication system between a control station: and a plurality of outlying stations together with certain signal arrangements which require an acknowledgement on the part of the attendants at each of the outlying stations. I

It isanother object of the present invention to provide a loudspeaking telephone communication system between a control station and a plustation or group of stations together with a common group of stations, and communication may be had with all stations associated with the system. l

Still another object of the present invention is to provide combined telephone and loudspeaking communication between a control station and a plurality of outlying stations wherein theloudspeaking system takes precedence over the usual telephone communication facilities by automatically removing the telephone set at thecontrol station and the outlying station when loudspeaking communication is beingused.

Still another, object of the present invention is to provide reliable communication service between a control station and a plurality of outlying stations, each of which is provided with auxiliary power equipment arranged to be automatically switched on or switched into service upon failure of the regular equipment and an indication or alarm is to be given which requires acknowledgement on the part of the attendant at the station.

In accordance with the present, nvention individual telephone communication is provided be-;

tween a control station and an outlying station. Either station may signal the other station that telephone communication is being desired. In

addition loudspeaker communication is provided between the control station and each or all of the outlying stations. While many of the features of the system to be disclosed herein may be used for various purposes they will be described,

to show one practical application, as being applied to a fire deparltmentw The control .station-isprovided withregular and emergency'eguipmentyas;

for example, two microphones and two amplifiers are provided for the loudspeaking communica tion feature of the system. Either of the microphones may be selected by the attendant atthe control station and either of theamplifiers, likewise, may be selected. In addition, the arnplifiers? are arranged to be automatically switched inrthe" event that the regular amplifier is not operating properly. A signaling system ;is-"provided-whichinforms the attendant of this change-over;

. Since reliability of communication is the prime characteristic of- 'this system; numerous devices and systems are prov'ided fon periodically or continuously testing the lines and the equipment possible'raults: A -continuous open-circuit test is provided by a relay which is responsive to-aade'crease in" line cur-rent below a predetermined amount -toactuatea" signal at the control station and at the -outlyingstatiorr associated with that' line; JSi-milaziy; a continuousshortoircuit t'est'i's pro-vided at eachstatiom' At the control stationac relay responsive to --an' increase in line ourrent above a prodstern-lined amount tors; and--to-pr'oy=ide thisprotective'feature'a testing circuit is arranged to test periodicallyatfrequent intervals-eachconductor of eachdine'for ground condition;- This accomplished by the use-ofsuitable switch me'ohanismwhich discon nects each line fi'om'= the" common "battery "source and tog-ether with an auxiliary; source applies a ground test-to each conductor: Upon occurrence providedat the-control station. I

'- Iloudspeaki-ng communication" is arranged for selective-operation with a single outfyin'g station, a group of outlying stations, ,or all outlying stacf 'a-ny ground condition 'a suitable indication is 'tion's'; 'Ilr'e" loudspeals'ing communication takes priority, over ordinary telephone"communication,

andwllen the-'-loudspealiing' communication systern" isset into operation means are responsive to thisoperationto disconnect" at" the control station" the* telephone set and disconnect at each of theoutlying stations thetelephone' set. 'Tlieloudspeaking"communication"is in only one direction from thecontro'lstation' to theoutlying stations.- In'orderthat therebe'no' d'elay, particularlyivli'en a group or stations orall stations are being; called, "in determining as to whether each of the called stations has received the communication; ea'clioutlying'" station is provided with 'meansfori acknowledging the loudspeaker communication; f'lhis means willrequir'e a minimum of attention and operation on the part of an at- 'tendantat'th'e' outlying station and will. require no immediate attention from the attendant. at the control station: This is' accomplished'bypro- 'viding ant impulse transmittin device which 'transmitsia'series of impulses to the.'contr.ol'-sta- 'ti'on. This'may comprisea dial actuated'transmitter which sends a predetermined number of impulses. At the control station these impulses are received by an energy storage circuit including a capacitor which is charged to a predetermined value whenever the proper number of impulses has been received from an outlying station. In response to these, a signal is displayed at the-control: station which at aulate-r time may bereleasediby the attendant ratith'ercontrol sta-v tion.

The control station is provided with a plurality of amplifiers each of which is tested at frequent intervals by a testing arrangement which transmits a: series of audio frequency impulses through reaoh amplifier, one at a time. If an amplifiersfailsato transmit a certain number of these impulses at a predetermined volume level anindica'tion' willhe given that the amplifier is not operating properly. If during test the normally used amplifier is not operating properly, the standbyflampl'ifier will beswitchedautomatically 7 into the operating circuit and an indioat-ionwill be given-accordingly. e t

In addition to the frequent period-ictests-of the "amplifiers at the" control station; periodic testsof -lesser frequency areprov-ided" for-the entire" loudspeakihg communicationequipment-of the system. At these'times each o f'--the';-ampl i fiers-is' again placed into operation; one at-a time, and a-senesor audio-frequency impulsesis-trarrsmitted tweachpfthe outlying stations. Th'e r'e ceip t of these i'mpnlsesat the 'outiy-ing stations is --acknowledged by the same impulse transmit ting arrangement" by which" loudspeaking voice communications are'acknowled'ge'di Thus'periodically operativen-ess of the "entirecommunication systemis'determined'i ln'additionto the t'elephone communication andthe loudspeaker communicationprovide d between acontrol stationand each of a plurality of outlying-stations, there is provided a group-of stationswhich are arranged to receive-only loudspeakercommunications. Such stations; for example; maybe" the-fire commissioner, waterand power companies; newspapers; etct, which, nowever; ,do not "reuuirejthe" elaborate equipmentmec essary'to in'sure"service',reiiability; Such stations 'arearrangedftdreceive allloudspeaker'communications whetherdirected-toa single outlying-station; a group'of outlying stations; or'alI of the outlying stationsu IIlbIdCr" that a single-"amplifier might behsed to" feed any one" or more of a1- pluraiityor lines without, requiring isolation equipment such as isolating amplifiers' for each line, a method? of couplingt'the lines to the amp-lifierisprovi'ded so that. the speech powe'r delivered toeach of the lines win e! substantiallyindependent or the number oflines connected to; theamplifier'and also independent'ofthecondition of the-various connected lines. "Thus, for exampleyifat *atime 'when loudspeaker communication is" heingj';di-

the: lines is. either short oircuited or ground d, 7

there will be no appreciable -effect upon the am- 'plifier'at a" controrstation; This' is accomplished lines is provided witira'ser'ies impede ,is large compared to the paralleliimp M the line but not sufiicfently'largeto" appreciably by providing, an amplifier having a slightry greaterfampl'ificatiomfactor than' wouldbe 'required' if" isolation devices or' circuits vvere used and'by' operating'tlref amplifier intoaterini-natiiis ies'istance which is'fllo'w compared to the-parallel impedance, of thev various; lines? Each of the w nce of increase the powerrequired per line to to its original operating condition.

under separate topic headings.

apredetermined-level'tothe line itself.

In order that power be available at all tim'es for the communication system, auxiliary power maintain equipment is provided at the control station and at each of the outlying stations. Whenever the auxiliary power equipment at any station 'is automatically switched into service due to the failure of the primary or commercialpower source, an alarm indication is givenwhichmust be acknowledged by the attendant at the station. .If the failure of a primary energy source ismerely 'an interruption, or is i of such nature that the nected to the -conductorsN233 and N234 of a' attendant is not required to take steps to correct thefault, nothingfurther need be done, but when the primary powersource is restored to service an alarm indication will again be given which requires acknowledgment on the part of theattendant so that allequipment may be. restored The novel features believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects I and advantages thereof, will be understood more readily by reference to the followingdescription taken in connection with the accompanying drawings in which Figs. 1 to 9, inclusive, when combined in the manner illustrated .inFig. 11, illustrate a communication system embodying the present invention; and. Fig. 10, diagrammatically illustrates certain connections forming a part of this systems i i Telephone communication system The present invention, which is particularly adapted" for use by such organizations as fire departments and police departments, is arranged to utilize a battery source which is also to serve for certain other purposes which, however, require that no ground be connected to this battery. This battery has been indicated in Fig. by the reference character 462 and certain operations in the system are augmented by an auxiliary batindicated by a symbol such as a large circle to gether with the appropriate polarity indication. The auxiliary battery terminals have been indicated as rather small circles together with the appropriate polarity indication. The system herein shown-and described has numerous features which subsequently will become apparent, and for the purpose of portraying the salient features as simply as possible these will be described Therefore, while the present system provides also loudspeaking communication for dispatching information to various outlying or remote stations, such as fire houses, ordinary telephone communicationis also provided, and this will be the first feature to be described,

Thecontrol station is provided with a tele- Each key N H0 is of the, three-position which are connected through break contacts 256 and 253 of a relay N250 to the primary winding of atransformerN228. The transformer N228 is provided with two secondary windings N2 I 9 and .a capacitor N232.

N2 29, the adjacent points being interconnected by The outer extremities of the transformer windings N2l9 and N229 are contelephone line which extends to an'outlying sta tion N400. Only one communication channel has been shown in the drawings as extending between the control station and an outlying or remote stationpalthough it is to be understood that the system contemplates the use of :a number of rebe multiplied by the total number of stations,

which may be N in number; tobe provided for the system. At the outlying station N400jthe telephone conductors N233 and N234are connected through the break contacts 443 and 444 of a relay LS440 to'a telephone set which includes the usual induction coil 434, a transmitter 435, a receiver 436, and a receiver switch43l. The receiver switch 437 is provided with the contacts 438 and 439 which are arranged to interrupt the circuits through the transmitter and receiver and the two windings of the induction coil. Interposed between the said contacts 439' and one winding of the inductioncoi l 434 is a capacitor 458 arrangedlto beshort-circuited by aswitch 459. The outlying station is alsoprovided with a source of energy 414 in the form of a storage battery arranged to'be maintained at proper charge by a charging device 5 which. is energized from the conductors 4 I 6 which are connected toa suitable source of commercial power or alternating current. nected to a choke coil 429 which in turn is connected to the telephone transmitter 1435.. ..The

common juncture between the choke coil 429 and capacitor 433 which is connected to the other side of the battery 414. l The choke coil: 429. and the capacitor 433 serve to smooth out any ripple which might appear across the battery 4l4 when the charger M5 is bringing thebattery: up to proper energy level. i I 1 If the attendant at the control station desires telephone communication with an attendant. at the outlying station N409 the first operation performed is to throw the switch N I ID to the left,

thereby to break the contact I 13 which, itcwill be seen, is connected to the positive terminal of the central source of energy. Thi interrupts the connection between thepositive terminal of, the

, regular exchange battery and; a conductorx,-1G4

falls below a predetermined value; sequently become apparent, these relays form a which extendsthrough break contacts 323 of a slow-operatingrelay N32U,,to a relay, NLO30B. Ihe circuit from the relay NLO303 maybe traced through the conductor-235,. the winding N229, of the transformer N228, the line conductor N234 to the outlying or remote station where the conductor N234 is connected to a winding 449 of a' transformer 454. The other. terminal of the transformer winding 449 isconnected through interrupter contacts 441, a relay LO430, a relay LS440,the Winding 44B of the transformer 454 to the other line conductor N233 which extends back to the controlstation. Conductor N233 is connected through the transformer winding N2l9, the conductor N265, a relay NLSSIO, the break contacts 325 of the relay N329, and aresistor 3 l3 tothe negative side of thecontrol station battery. The relays NLO390 at the control station and LO430 at the outlying station are arranged to release theirarmatures whenever the line current As will sub- The battery 4|4 istconi previous conditions.

part of a continuous testing arrangement for y determining the occurrence OfLanopen-circuit com ditionon the telephone 11116.".T118 actuationeof the key NI ID at the-control station which: brought about the. release of thesetwo relays is,- however,

for the purpose of notifying the attendant atuthe outlying station that communication is-being. de sired. The. relay LO43B at. the outlying. station, therefore, drops its armaturesothat the break contact 432 thereof is closed. Thebreak contact is connected in. acircuit which extends through. break contact 4520f a key- 450 to a:.bell 453, .whichin turn is connected through-the make contacts. 42I of arelay-420, which contact is connected to one .side of the alternating. current source 6. Theother side -of..the alternating current source 4| 6'is connected through the make contact 423 of the relay 4-20 to the. armature of the break contact 432 of the relay. LO43D; and hence alternating current energy is supplied to the bel1.453 thus giving an audible'signal to the attendant. The attendant knows that when the signal given by the bell v453 is of'short duration, or is intermittent, the control'station is-.calling. The bell 453 also serves to indicate certainabnormal conditions which subsequently will .be-

comeapparent. The attendant at the control station having for a. short interval thrownthe switchNl NJ. to the leftnow. throws the switch to the right which is talk position, wherein the contacts H I and. I I2 are closed to connectthetelephone set ID! to the conductors H12 and, IE3, whichin turn are connectedas. previously de scribed with the telephone lineextendingtothe outlying station. As soon as. the. switchNl lilis actuated to permit-the break contactl l3 to close, the relays NLOBOU at" the control station and LO430. at .the outlying stationagainpick uptheir armatures, thus-restoring these circuits to their The attendant -.at;the. re.- mote station N400: thereuponremoves the re.- ceiver-436 to close the hookswitchf43'l whereby communicationmay now be hadlbetweenthe two stations. g

If the attendant. at theoutlying station N400 desires-to signal the attendant at thecontrolstation, the receiver 436 is lifted to actuate-the :hook

switch 431 and the switch 459 is-momentarily closed, which places -a short-circuit'acrossthezline conductors N233 and N234. A circuit may.. be

traced from the switch 459 through: themake contacts 438 and 439 of. the switch 43.1). the. re.-

station; Thus atthe. control. station the. relay NLS3|0 is actuated, thus closing make. contacts 3| I which are connectedbetweenthe positiverside :of..the central energy. source and. a. conductor 312 which-extends through the signal. lamp N524 and break. contacts 513: of a switch 5!!) to an alarm .or buzzer device 521 which is connectedto' the negative side of the. regular-exchange battery. Thus. the. signal :lamp N524 isilluminated' which indicatespa line short on the telephone line. ex? tending. to. the outlying station N403,sincea number. of; theselampsare-provided, .each. for a different telephone,line;.- The, audible ,signal or. buzzer 521. isconnected in common circuit relation to .all

Loudspeaking communic ationf silstem" j -Loud'speaking communication is also provided between' the control station and one or more of theremote stat-ions. For this purpo'se there is provided at the control station certain equipment which includesha microphone I05 and -a stand-by microphone S; eith'er'of which may be used bythrowing a switch l2llin the proper direction to 4 close contacts I 22 or l 2|. crophones are arrangedto be connected by a pair of conductors In! which includes a series resistor or impedance I35 to an amplifier 21M or a standby amplifier SZBI. .The two microphones and two amplifiers-are provided so thatin the eventone of the devices .fails to function'properly; theother device .will be available. to. insure reliable com.-

.munication for the. loudspeaking dispatching. system.; The'amplifier Zlltis normally the amplifier usedand the output thereof .is connectedv toaresistori 225, the value of which .isv relatively. low as compared to theirnpedance. of any, or all. of the telephone lines whichcmay bev connected to the amplifier. The impedanceorresistor 225-;is connected .to the break contacts 216 and..2l8 of, a

connected through the break contact: l;l3.of.-.'the I switch NI l0, theconductor lild the break contact 323 of the-relay. N320, the relay NLO3H0,

whichis connected through the conductor 235,

the transformer winding N2291 0f the. trans former N228 to the line conductor:N234=which,; at.

' ginal type arranged .to'sbe energized wheneven'the line current exceeds a predetermined amount, which is the condition obtained byan action-such asthe closing of the switch 459- ,at the remote- ..relay flfl; Y These contacts are eachoonnected to resistors N223 and N 224 which have a value which is. relativelyhigh compared: to the. parallel. inipedance of-all of the telephone lines; :Theseresistors N223. and N224- are arranged to-be connected: in series withtheir correspondinghtelephone lines as is thecase whenthe. makecontacts 255 and 25Lof a'relay-N250'are v'clr'isedmo connect the: amplifier- 231i to the. transformer. N228. n

plurality of individual keys correspondin to the individual telephone; lines and remote stations .is

provided. These keys N501;each have a.break contact 5.08:connectedto.a conductor51|8,.and a make: contact 509. connected. to the. positiveten minal ofthe regular exchangebattery. The switch armlotthe switch N531 is. connectedtoc a conductor-.254, which isconnected through asignallamp N5l1 to the negative terminal of the regularexchange battery, and also to relayN250. which is also connected to. the negative terminal of. this same battery. 1

h t will now'be assumed that the attendantflat the control'lstation.desires to call theremotejstation.N403,- whereupon .thcrswit'ch N 5011. is actuated ;thus.to supply potential to the signal lamp N511 and-to the relayN25ll; The relay N253 upon being ,actuatifcloses make contact 251'. tosupply'enz-ergy tea relay. 300. which is provided'withaplu- The mirality of make contacts such as Bill, 602? and .603

which are arranged to connect a group or groups I of stations to the amplifier whenever the'control station communicates with any one or more of the remote stations; The purpose and operation ofthis arrangement will subsequently be de-. scribed. The relay N250 closes contacts .252 and I supplies potential to a conductor 238 which exthe resistors. N223 and N224 to the amplifier 20I, I

providedthat this amplifier 20I has not been switched out of, service. If the amplifier 20I has been switched out of service the amplifier S20I is in service by virtueof operation of the relay 2 I which will close the contacts 2! and 2H. At the time that the relay N250 operates, contact 254 is closed to complete a circuit from the positive side of the auxiliary battery supply 463 through a circuit including a resistor. 221, the winding N220 of, the transformerNZZS, the conductor N234, the winding 449 at the outlying statio-n,the contacts 441, therelay LO430, the relay B8440, the winding 448 of the transformer 45 i. the other line conductor N233, back to the control station, through the transformer winding N2I9, the conductor N285, the relay N LS3I0, the break contact 325 of relay N320, a resistor 3 !3 to the negative side of the regular exchange battery, the positiveterminal ofwhich is connected to the negative terminal of the auxiliary battery 433 shown in Fig. 10. This, therefore, connects into circuit the auxiliary battery463 thereby to produce an increase in the current flowing inthe line circuit, which causes the marginal relays NL S3I0 at the control stationand LS440 at the remote station to be actuated. a i H I At the outlying station the relay LS440 closes contacts 44I which. are connected to. an amplifier 46L to complete. a circuit which may be in the anodepower supply of the amplifier. The contacts 442 are opened which are connected in a circuit including a resistor 456 normally connected across the conductors extending between the amplifier 46I and the loudspeaker. 451 so as to prevent, duringnon-operation of the loudspeaking communication system, the reproduction of certain inherent amplifier noises .which may for convenience, be called singing. At the control station aswitch I30 is actuated to the left to close both contacts I3I fand I32; This completes two circuits from the positive terminal of theregular exchange battery, one of which includes a conductor I36 which extendsto a relay 830 which closes its contacts 83 I and 832 to supply energy to an audio frequency tone generator 845. The tone generator 845 is connected through a resistance or impedance network 825, 826 toa pairof conductors I23 and I24 which are connected across the resistor I05 which is in series with one of the microphones, such as. I 05, andhence is effectively across the input of one of the amplifiers, such as I. Thusaudiofrequency energy from the tone generator 845 is being supplied to the amplifiers. At the same time the actuation of the switch I has completed a, circuitf'rom the positive terminal of the regularexchange battery through the contact I3I and a conductor .I I8- to a relay 220 which is connected to the negative side of the regular connected in a circuit includingbreakcontact 2I4 of relay 2I0, and in the anode current supply cir- ,cuit of the amplifier 20I.- If, for example, the.

stand-by amplifier S20I were in operation, the relay 2 I0 would be energized so that contact 2I4 would be broken and contact 2 I3 wouldybemade, whereb the closing of the contacts 22I of the relay 220 would complete the anode current sup-- ply circuit of the stand-by amplifier S20I. 1 Thus audio frequencyenergyis now passing through one of the amplifiers and ,is being transmitted through the amplifier. at the called station to the loudspeaker. The attendant at the outlying station thereupon awaits the communication 'tobe expected from the control station. 1

. The attendant at the control station makes the necessary dispatch over the loudspeaking system to all remote stations connected to the amplifier at that time. The dispatcher, however, must know whether or not each of thestations thus connected hasreceived and understood the dispatch given. In order that an acknowledgment of the dispatch shall not appreciably delay. the execution of the actionrequired by the dispatch, means are provided at each outlying station for acknowledging the dispatch. Thismeans preferably comprises a dial having a single finger h'ole corresponding to the zerodigit. This dialyactuates the dial make and break contacts 441fto. transmit a predetermined number of pulses over the telephone line comprising the conductors N233 and N234 to the control station. Since the contacts 441, when opened, place an open-circuit condition on the line, the relay NLO300 at the control station will respond to this momentary open-circuit condition each time" that a pulseis transmitted. Thus the contact 30l is broken which is connected by conductor 3021to a slowrelease relay N130 and to a rapid-release relay N which is connected through the contact 13I of the relay N130. Because therelay N is of a slow-release nature, the armature thereof does not move andhence contact 132 is not made and 12I are closed, the capacitor 1I2 will accumu late a charge having a voltage sufiicient toybring about energization of relay N1I0, whereuponits contacts III will be closed thereby to illuminate the lamp N525 which in turn is connected through the contacts 5 of a key5l0 tothe positive terminal of the regularexchange battery, whereupon the relay N1I0 is lockedinto operation. The illuminated lamp N525 therefore constitutes an acknowledgment indication that the corresponding outlying station, such as N400, has received and understood the dispatch. A number of lamps similar to N525 are each illuminated-in response to each of theoutlying stationsfreturning their acknowledgment. The attendant at asuibsequent time may release all of the acknowledgment "such as N525, and all of the. relays correphone line conductors N233 andN234.

spending to N1l0,"by throwing the switch 5m to the left whereby the contacts5ll will be broken, thus'to interrupt thecircuits and restore them to original condition.

I 'In a system of this sort it furthermore is necestion. In the previous description of com'munica- I tion to an outlying station'it will be remembered that the attendant actuated a key N501 to the left, thereby to energize the relayNZ 50 whichinterrupted the break contacts 256 and 258 which were connected to theconductors I02 and I03 extending to a key-NI l0 whereby theattendants telephone set could be connected. It therefore is apparent thatthe operation of the relay N250 serves to disconnect from any telephone line the telephone set at the control station. At the same time the-relay N250 completed thecontact 254 thereby to supply additional potential to'the telephone line so as to'bring about theoperation at the outlying station of the relay LS440. The operation of the relay LS440 opens the contacts 443 and 444 thereby disconnecting the telephone transmitterand receiver from the tele- This operation of course occurs at all stations which arearranged to be connected to the control station by one or more selective switching means at the control station suchas the key'N501 or certain other keys whereby certain groups of stations or all stationsin the system may be connectedto the amplifier at the control station.

1 It may be desirable at times to: call a certain I group of stations and for this'purpose a plura'lityof group keys G500 is provided. The key G500, when actuated, closes contacts 50! and 502, the latter being connected to a signal lamp G503 corresponding 'tothat group. The closing of the contacts 50! places the'positive terminal of the regular exchange battery on a conductor 53B which'extends to a group re1ay"B|'0. Each group relay is provided with a plurality of contacts, one of which is shown-at 6| I. The closing ofeach of the contacts corresponding to the contacts'6ll -brings about the operation of corresponding relays such as N250 for each station included in that particular group. This will be appreciated by following the circuit which extends from the contacts 6| I through the conduotor 518, the break contact 508 of one of the keys N501, the conductor 254, to a relay N250. Therefore the corresponding relay N250" is actuated in response to the operation of the relay 6l0. i

If it is desired to have all stations'connected at the same time tothe control station, a. single key such as AS504 'is'actuated to place the posltive terminal potential of the regular exchange battery upon the conductor 531whereby the allstation pilot lamp AS505 'will be illuminated. The conductor 531 is connected to the all-station relay 620, of which sufficient relays are provided so as to connect all of the stations into the cir- 'cuit. This is accomplished by having such rewhereby the corresponding station in turn will acknowledge the dispatch lamp N525 *isillur'ninated.

Whenever an individualstationysuch as N400; or a group of stations such'as controlled by'the relay 6l0,-or all stations such asscontrolled by the relay620 are connected to theamplifierat the control station, a common group of stations is also connected to the amplifier. Such:grol1p may comprise a plurality of stations corresponding to N400which are controlled by one of a plurality of contacts corresponding to contacts 603- of the relay 600, and also a number of other I stations controlled by the contacts '60! and-602 of the relay 000. This latter group of stations comprises stations such as 540 each provided with an amplifier MI and aloudspeakerfl54'2 connected by conductors 543 throughresistors 63land 632 to the contacts 60l and 602 of the relay 600. For example, such loudspeaking stations corresponding to 540 may include stations such as the newspapers, the water and power companies, etc. 1

Continuous line testing Service reliability being one of the prime characteristics of a system of this sortrequires that each of the telephone lines to the remote stations be maintained in proper operating condi-' tion. In order to determine this operating con dition an arrangement is provided for continuous'line testing having open-circuitand shortcircuit conditions. At the control station each line corresponding to the conductors N233 and N234 is interconnected with relays correspond ing to NLO'300 and'NLS3l0. The-relay NLO-300 continuously detects acondition corresponding to open-line condition since the relay NLO'300 will drop its armature as soon asthe line current drops below a predetermined value thus opening its contact 30| whichis connected to a con duotor302, thereby to deenergize relays'N130 and N120. The relay N130 opens its contact 133 and closes its contact 132, which latter contact is connected to conductor 52!, whereby, positive potential issupplied' to the conductor to illumi nate the line-open indication'lampN5l9 which is connected through break contact 515 of'the switch 5H) to an'audible alarm orbuzzer 528 connected to the negative terminal of the regular exchange battery. Thus the signal lamp N519 indicates the particular-line which has an open-circuit condition thereon and the general audible alarm device 528 signals the operator that such condition is present. I

The control station is also informed ofa lineshort condition occurring on each telephoneline by operation of the corresponding relay 'NLS3I0 which is arranged .to be actuated whenever the line current is increased above .a predetermined value. When this occur s the contacts '3 are closed, thereby to place the positive potential of the regular exchange batteryupon a conductor 3|2 which is connected .to illuminate the lineshort indicating lamp N524, which in turn is connected through the break contact 5I3. of the switch 5| 0 to a common audible alarm 521 which signals a'line-short condition. Whenever either a line-short condition or an open-line condition occurs the attendant. at the controlstation having noted such condition may thereupon throw the switch 510 to the right thereby to acknowledge the trouble condition and to deenergize the particular audibleand visual signal devices.)

At theoutlying station a relay LO430 is arfails.

ranged to be deenergized whenever the line contact 423 of the relay 420, the" contacts 432 i and 452 to the alarm bell 453, which in turn is connected through the contact 42 I of therelay 420 to the other side 'of' the alternating current source 4|0. The, outlying station attendant thereforebecomes aware of some difiiculty on the lineand this may be acknowledgedvby throwing the key 450 to open the contact 452 and to close the contact 451. If subsequently the line is restoredto its'orig'inal condition the relay LO430 will be energized, thereby closing its contact 43! so as toagain supplyalternating cur rent energy to the bell ,453. The attendant thereupon acknowledges the returnof the line to its'normal condition by throwing the key 453 toopen the contact 45I and to close the other contact 452. i i a 1 If now, however, a line-short occurs across theconductors N233 and N234 the line current, at the "control station will rise" above a predetermined amount/thereby to actuate the relay NLS3I0. This is due to the fact that the control station is provided with the regular exchange battery and the short-circuit of course occurs at some point just beyond the control station. Due

to the short circuit, the control station exchange battery cannot supply line current tothatportion of the line beyond the short circuit, and hence attheoutlying station the line current thereby causing the relay LO430 todrop out of the circuit. The alarm 453 therefore'isactuated Periodical line testiac Becausethe control station exchange battery is ungrounded, it is necessary to provide a means for periodically testing each conductor of each telephone line for ground condition by apparatus which does this by the use ofanauxiliarybattery. The controlstation is provided with a power supply which includes a connectionto a commercial sourceof energy; and an auxiliary power supply is provided which is automatically switched in whenever the commercial source This source of powenwhich supplies energy to the amplifiers 20| and'S20 I is connected by aswitch 824 to a timing circuit which includes asynchronous motor 321 which drives through suitable gearingyindicated by the rec- .tangle 328, a pair of cams-835 andt829b The cam 835 is driven at a rate toprovide one revolution every few minutes, for exampleeveryfive minutes, and the other cam B29 is driven at a rate to provide one revolution in several, hours,

for example; every four hours. The cam 335 relay contact 822 to the parallelconnected: relays 140 and 150,. the latter relay being a slow-opera fore the relay 150' a circuit iscompleted from the positive terminal of the regular exchange battery through the make contact 14! 'of this relay, the

break contact 15! of theslow-operating relay 150"tc relay 160 which is connected through a current limiting resistor 162 to the negative side of the exchange battery. At the same time a circuit is also completed by way of the condu'ctor362 to'a steppingrnagnet 310 which is connected rtothe negative terminal of the exchange batteryp- The wipers 312, 313 and 314 associatedwith the magnet 310 are arranged to advance one step when the magnet 310 is restored. When relay 150 operates after a short delay contacts 15| are opened to interrupt the circuit for magnet 310 1 thereby allowing this magnet to restore and move the wipers one step in the' counterclockwise direction. As soon as the magnet 310 has moved the switch arms for ward one step, one of a plurality of relays, such as N320; is actuated so that in response the contacts 322 are (made, thereby to energize a slowoperating relay 340. The relay N320 has also interrupted cdntacts 323 and 325 thereby disconnecting the telephone line conductors N233 and N234 from the regular exchange battery,

and these conductors .have been connected by contacts 333, a current limiting resistor 328, test battery 333 contacts 323, relay winding NLO3EIO, conductor 235, winding N220 and line conductor N234. At the same time that the slow-operating relay 340 closed its contacts 34! the contacts 342-wereclosed which energizeda slow-operating relay 330 which operates ashort time later and interrupts the contacts 333 and closes contacts 332, thereby to connect the rapid-operating relay 350 from ground through the contacts 345 and 332 to a'currentlimiting resistor 329 which isconnected through the test battery 303, resistor 321, contacts 323, winding of relay NLSSHJ, windingNZlQ to the line conductor N233. The relay 350 iswt-hus successively connected between ground and each of the line conductors N234 andN233to test forground. If the line conductorlbeing tested is grounded, the test bat- .tery 303 will operate relay 350.

'When-the'relay 330 closes contacts we slowoperating relay 360 is energized'closing contacts 36! to complete a circuitfrom the'positive terminal' of the exchange battery through relay contacts 32l, 33!, 33! and magnet 310 to thenegative terminal of the exchange battery. Magnet 310 operatesto condition wipers 31.2, 313 and 314 for operation. Relay 330m closing its contacts 363 completes a circuitfor energizing the slowoperating relay 330. Relay 380, upon operating,

shortly thereafter, interrupts at contacts 38 i the ating relay. Since the relay 140 z-operates be- 2 energizing circuit for the magnet 310, whereupon the wipers 312, 313 and 314 aremovedone step in the counterclockwise direction and into en-,

gagementwith contacts terminating the circuit for the next succeeding rela correspondingto relayN320.

Aft'eruthe initial starting pulse has been reof cams-839, 803 and846.

ceived "by the vmagnetr3l'llrfrorn relays I430 and I50, the continued intermittent operation bftthe wipers 312, i313 and 3:14 is maintained, by :the

magnet 31.0 entirely under'the'control' of relays N320, 330", 340, 350, 300 and 1 380. These latter relays perform in the above-explained manner, causing tests to be made upon all --of the lines in the system in succession with the exception :of thoseflines which arein'use for the-transmission of loudspeaking service. After onehalfrevolution of the wipers the opposite ends of (thBiWiPl-EI'S 312, 3ll3-and 314 engage thenormalscontactsand as1no relay corresponding to relay N320 is connectedr'thereto, operation of the wipers is discontinued and a testing cycle is completed. vA new cycleisinitiated as explainedzabove by roperation of the timing cam 835, whereby contacts 036 are againclosed to complete a circuit for relays'l40 and I50.

.If, however, a ground condition is found on either of the line conductors N233 or N234 this will .be reported prior to the operationiof :the slowoperating relay 360. Since the relayi350 will. close its contacts 35l, whereby the 'switch'arm 313 will engage conductor 334' which'is arranged .to energize relay N100, the1r'e'layNl00 willclose its contacts I! to supply potential to a 'conductor'5'35 which is connected through-a key N506 to the positive-terminal of the regular exchange battery, thereby locking in the relay :Nl00. The :relay N100 also closes its contacts 102 connected to the conductor 523 connected to asignal lamp 522, which is connected through'contacts5l5 of the switch 5") to an audible alarm device528'which in-turn is connected to the negative side 'of .the regular exchange battery; The attendant at the control station having become aware of the ground condition on one of thetelephone lines may acknowledge "this by actuating the switch N500 which will deenergize the relay N100" thereby also to deenergize the audible alarm device528 and the visual signal-N522. tion encountered on one of the "lines, however, must be cleared up, and until this is done a periodic audible warning signal will be given every five minutes by energization of the audible signal I 15, as will be described hereinafter;

It will be remembered that rat the time thatthe'cam 035 closed the switch contacts 836, that the relays 140 and I50 were energized in parallel. The're'lay M0,however, is quicker to operate than the relay I50 so that the contact Ml wasmade prior to the breaking of the contact I.5l.' Energy therefore was supplied for a short time interval to the relay I60 which attracted its armature thereby to close the-contacts I6! so that the relays 240 and 8 I 0 were energized. These relays are in parallel .and shortly after energization are locked-into operation. The relay-8J0 is also in a circuit which includes a motor 831 which drives a gear box 8-38 to which is attached-a plurality The cam 039 actuates a switch 840which, by the making of the contacts I "04!, locksinto operation the relays 240and '3 l0 and the motor'83I. If duringa previous test-by the-timing equipment :800 oneof the lines was found'to havea ground thereon a corresponding signaliwas indicated by-the lamp N522 and the avicircuit including:' the :negative terminallof. the regular exchange batterycormectedzthronghcontactaifli. lAccordinglyfiwhenzthe:next-test:period occurs, the acknowledgment switch .540 having been thrown to the right 'has :closed the-contacts 5L2 thereby to complete a circuitfromtherposixtive terminal of the regular exchange :battery I through conductor "131; the alarm device I 1.5, the

conductor I l 2 8, the, contacts-241- :of' the relay-24:0, and a resistor r245 to'the negative terminal; of theregular exchange battery. Thus the attendant -at zjthe 1 control station is intermittently at five :minute-intervals warned of line trouble-on onezonmoreofithe telephone lines.

If at the time 'that'the timer -800 i sto make its periodic five 1minute tests any one or: more ating withthe switch arm 314. The-switch arm 314, upon'engaging'a contact being supplied'with positive potential, will thereupon again energize the stepping relay 310 so that itadvancesthe switch arms 312,313 and 314 to the next suc- The ground condialarm device 528, which was acknowledged by of the key N506 when a grounded line is indicated by the;lamp N522 and the buzzer 528, the

buzzer 528 will be disconnected at contact 5L5 but ,the; lamp N E-22 will remain Lilluminated from ceeding contact, :thereby j preventing the remaining apparatus which'includes'the auxiliary bat"- tery and the-relays N320, 330,340,350, 360 and 380, from operating. Otherlines', however, which do not have a potential applied through conductors corresponding 'tothe conductor 238 are subjected to'the ground test. At' thesame time-that' relay N250is-energized, thereby closing its contacts 253, the conductors 23B and 231 are connected together which are across the relay I60, thereby short-circuiting this relay. Thus whenever thetimer'800 begins" its periodic operation, thereby energizing relays 1'40 and I50 which normally would provide'ashort period of energization of=the relay 160; which, however, has been shortcircuitedibecause of loudspeaking communication beingcarriedonover one or more of 'the'telephone lines, will not be operated and hence the relays 24-0and 8H] are not energized. .As' a result of this thenmotor 83! also is 'not energized and hence that part of the testingapparatus does. I not come into operation as long as the loudspeakthe line ground tests, there is also provided an arrangement for testing each of the amplifiers '20l'an'd' $20!. The timer 800 having 'closjedthe contacts 836 of the switch operated"by the cam 835, has energized relays and I50 so that for l v a short interval the relay I60has been energized so as to look into circuit the relay-8R0 and-the motor*83'|. The relay 240 is also lockedinto circuit and this relay closes its contacts244' thereby to energize relay 220 which closes its contacts 22! and 222, whereby the anode circuit of the amplifier 20l is completed thereby conditioning this amplifier for use. At the same time the '-contacts 243 are interrupted and contacts 242 are closed which momentarily interrupts the circuit offthe relay Y230 :and again closes it." The relay 240 also prepares, a circuit from'tlie' negative terminal of the regular exchange lbattery through resistor 245:and relay 'contacts 24l to conductor I28 which is connected to icontacts l52 and I54 of switch I50. I I I I In the event that priorto the periodic amplifier test the-switch I50 has been actuatedin either directionto acknowledge the failure of one or the otherof the amplifiers, as, for example, by I I "in this case is in a circuit extending from the positive terminal of the regular exchange battery through contacts 242, the conductor I26 and lamp II4 which is connected to'the negative terminal of the regular exchange battery.

The test continues, and motor 831 by means of the cm 839 actuates' switch 840 which by coni I tacts 84I has connected in the motor 83! across the regular exchange battery. The switch 840 has also closed contacts 842 to supply energy to an audiofrequency tone generator 045, the output of which is connected to a circuit including a pair of resistors 825and 8 26} the latter resistor being connected across the'conductors I23 and I24. The cam 6 43 is provided with two groups of detents, each four in number, so as to close the contacts 644 wherebyfor short time interdesigned to operate.

relay 260 having been closed apply positive potential contacts 902 of the relay 900.

tingithe attendant at the control station to so regulate the volume of -his voice as to provide intelligible reproduction without greatly exceed- 'ing normal volume level at which the system is The contacts 26I of the from the regular exchange battery through conductor 263, contacts 903 of the relay 900, contacts 922 of a relay 920, toa relay 925 which is connected to the negative terminal of the regular exchange battery. "This brings about energization of the relay 925 which pullsup its armature to close the contacts 926; I Positive potential therefore is now applied at both terminals of a relay 920, one potential being supplied through the contacts 926 of the relay 9250and I the other potential being supplied through the The cam 043continues to rotate so that after a short time the contacts 844 are opened, whereby no'longer is there applied to the amplifier any audio frequency energy sufiicient to maintainqthe energization of the relay 260. Thereupon the posivals the tone generator 845 will be connected to V supply energy to the conductors I23' and I24. The conductors I23 and l24-are connected across th resistor I06 which isin the input circuit to the amplifiers 20I and SZOI. The cam 846 dur ing one half of its revolution closes contacts 841 which are connected t contacts 8 of relay 0I0 which are connected toconductor 818 which leads to arelay900. Therefore the relay 900 is energized so that it closes contacts 902 and 903, the latter [contact being connectedto conductor 7 263 which extends to the contacts 26I of a relay 260. The relay 260 is arrangedto be energized by suitable vacuum tube circuits connected to receive energy from the loudspeaking amplifier then in use which is connected to the conductors 264. This device, of course, may be any one of a number of suitable arrangements arranged to be responsive to a predetermined volume level of the amplifier, whereupon th relay 260 will be energized. Each time that a short interval of inputof "the amplifier 20I-, which normally is connected for use, the energy appearing across the output is connected to appear across the eonductors 264, thereby to provide an energization of the relay 260 if the amplifier is operating to amplify the received signalup to a predetermined amount. It will be assumed that the amplifier has amplified the first pulse of audio frequency sufllcientlyto cause operation of the relay 260 conductors I38 connected to anindicating meter,

I09 which primarily is for the purpose'of permitaudi frequency is supplied bythe tone generator 345 through the conductors I23 and I24 to the l tive potential appearing on the conductor 263 is no longer applied to the contact 926 of the relay 925. Positive potential, however, is applied from the contacts 902 of the relay 900 to the relay 920 and through the contacts 926 ofrelay 925 which in turn is connected to the negative terminal of the regular exchange rbattery, whereby both of these relays are now locked in series circuit. .-The

relay 920, being energized, interrupts contacts '922 and closescontacts 92I. The cam wheel843 continues to advance, whereupon the contacts 844 again are closed thus supplying a short ina terval of audiofrequency energy from the tone generator 045 to the amplifierdzfll. If theam plifier is operating properly therrelay 260 again will be energized, whereupon positive potential will be applied to the conductor 263 and a circuit is now completed from the conductor 263 through the contact 903, the contact 92I, the contact 932 to the relay 935 which is connected to the negative terminal of the regular exchange battery.

This relay closes its contacts 936 thereby condiq tioning relay 930 for operation in-a manner simlar to thet operation previously described in connection with the relay 920; As soon as the cam 843 has advanced sufiiciently to again open the contacts 844; the relay, 930 will be energized thereby to interrupt the contacts 932 and to close contacts 93I. At the next succeeding tone innpuls delivered to the amplifier 20I the relay 260 again operates to apply potential to the conductor 263 whereby the circuit is .now from the conductor through the contacts903, 92'I, 93I and 942 to the relay 945 which is connected to the negative terminaloffthc regular exchange battery. This relay attracts its armature to close contacts 946 thereby toagai'n .prepare'a circuit for the energization of the relay 940 in a manner similar to the energization of the relays 920and 930. When the switch 844 is again interrupted the relay 940 will be energized, thereby tointerrupt the contacts 942 and to close contacts 94I which are connected to contacts 9 and I, the latter one having been closed \by the operation of the Relays 910 and 980 each were energized at the time that the relay 8I0 interrupted contacts 8I4 and closed contacts 8I3 which then were connected to the positive terminal of the regular exchange battery so as to apply thispotential to the conductor 815 which is connected to the relays 959 and 969 arranged in parallel and each connected to the negative: terminal of the regular exchange battery... The relay 95-9 operates: more.

rapidly than relay 969 which is slow-operating. Connectionis thereby completed from the positive terminal of the regular exchange battery through contacts 95l= to each of. the contacts 96l',

962. and 983 of the relay 969,. whereby the winding 9 1fi=ofthe relay'9l9 and the winding 9-85 of the relay 989 energized thereby to operate: these relays. At the same: time, prior to the operation of the relay 9&9v energy is supplied to the contacts 9'6I to a conductor 53! which extends to an audible. alamn device 529 .connected to the negative terminal. of the regular exchange.- battery. This .audible alarm when continuously energized informs the attendantof a testing condition-sub.-

cam 843 which closes :the. contacts 844. This fourth. impulse causes operation of the relay 269 whereby positive potential is appliedto the conductor 263. through the contacts 993, 921-, 93], 9M and 9M: to the contacts 911' of the relay 9'19, thereby to energize the winding 975 which is differentially arranged relative to. 'thewinding 916 which thereupon will bring about a release of this: relay. 1

'I'hecams connected to the motor 831 by the gear box 838 have now made one-half: revolution so that the cam 846: will actuate its switch to interrupt contacts 84.1 and to close contacts 848, whereby positive potential is applied to a conductor 849 to energize a slow-operating re1ay'9-l-9. Prior "to the operation of the relay 919 the relay 999 releases due to the interruption of the. contacts841. During the subsequent rotation. of the cam 843 successive: intervals of audio frequency energy are. supplied from the. tone generator 845 'to the conductors I23: and [24. The. relay 919, having operated, has closedits contacts 914*thereby' to supply positive. potential. to a conductor 11-9 which is connected. to relay 2l'9'which now operates to interrupt the anode supply to the amplifier 29 t by opening its contacts 2M and to complete the anode supply to the amplifier S291 by closing its contacts 213- At the same time contacts 2116 and 2l 8". are interrupted-and contacts' 215 and. 21 'l' I are closed so as: to disconnect the output of the amplifier 29k from the conductors 26-4 and to connect the output of the amplifier S201 to. these same conductors. The relay 289 therefore is now arranged to be responsive to the output of the auxiliary amplifier S291 whereby during the successive tone impulses the relay is successively energized; to bring, about operation of relays 929, 92 5,. 939; 935 949.- and 94.5 in a manner similar to the-previous operation since the circuit arrangement provided by the interruption of the contacts 993. of the relay"- 999 and. the closing of the'contacts 91-.31of. the relay EH9 isthe same as far as these relays are concorned. At the time that the relay 999- was re.-

leased all 'orlthese "relayswere deenergizedzbee causeof the interruption of. the contacts 992. For the first current impulse. applied; to the auxiliary amplifierSZM the: relay 9l=9.has prepared a circuit by the closing of its contacts. 9&2 sothat at. the termination. or :the first. impulse the relays 929- and 925 are locked into circuit..-Therefore it may now be. assumed that all. of'these relays. have. responded to: the firstthreeimpulses given-to the attendant at. the control station and the regular amplifier 291 will again be returned to service'since: the earn 846, upomcompletion of its revolution, will open contacts 848 thereby to deenergizerelay 9J0? so that-relay 2t9 is deenergized. The cams 83-9 and 843: having, completed one revolution open the output circuit. of the tone generator 945 and interrupt the energy supply circuitsto the tone generator, the motor 831, the relays BIG and 249 thus restoringthe equipment. to its original condition: prior to the test. a

lif the auxiliary amplifier S294 failed to receive and amplify at proper volume level all of. its impulses, th relay 999. would not. have been released whereby the contacts; 983 still. would be closed. Upon deenergization of the: relay 8li9 positive potential would be applied through the contacts 814 to conductor 913 which is connected through contacts 983 to conductor 5'34 whichis connected through a.- .signal lamp 532 to the negative. terminal of: the regular exchange bat,- tery thus to provide a visual indication. that the auxiliary amplifier isnot operating properly. An

audible signal is also provided byaconnection the circuit through the audible signal device I Hi.

If at the time that the next fiveminute testing period is: to begin the-spare. amplifier has notyet been: placed in proper operating conditiorr'the relay 249- will be energized thereby to connect the negative terminal of'the: regular exchange battery through the resistor 245 and relay contacts 241- to conductor I28v which now is connected to switch-contacts I52. and 1-53 'tothe signal device 1 H51, which in turnis connected by means of conductors I21, 228 and53'4, contacts 983, 91 3 and to conductor H9. The regular amplifier will receive its usual. test from the thou.- sand cycle tone apparatus and subsequently the spare amplifier will be tested. involves the operation or relay 919 which closes contacts 914 thereby to complete a connection betweenthe conductor H9 the positive terminal. of, the exchange battery, thus bringing about energizalticnof the signal'device H6 for thetime interval required normally to test the spare amplifier. Thus periodically every five minutes the signal device 6 will be energized to remind the attendant at the control station that one. of the amplifiers has not yet been restored to normal operatingcondition.

i If it is assumed that the amplifier 20I failed to receive and amplify properly all of its impulses, the relay 910 will not have beenreleased. Upon release of 'the'relay BIO positive potential will be applied throughthe contacts 8 to the conductor 8I6 and to both contacts 913 and 914 of relay 970. The latter contact 914 is connected to'co'nducto-r 533 which in turn is connected through signal lamp s532 t the negative terminalof the exchange batteryto indicate that the spare amplifier has been switched into operation. This "switching of the spare amplifier was accomplished by the application of positive potential through the contacts 913 of the relay 91B to the conductor I I9 which is connected to energize relay2 I 0. The relay 2I0 by the contacts 2I3 to 2I8, inclusive, switches into use the auxiliary amplifier SI. The 'relay 2I0 interrupts the contacts 2| I thereby to deenergizezthe relay 230 which is connected by conductor I through a signal lamp I I4to the negative terminal of the regular exchange battery. The signal lamp II4 normally is illuminated when the regular amplifier 20I is in use. The deenergization of therelay 230 pemnits the closing of contacts 23I to supply positive potentialto a conductor I21 which is 1 connected to an audible alarm device II5,which in-turn is connectedthrough contacts I53 and I5I of switch Iand through resistor I IT to the negative side of the regular exchangewbattery. The attendant at the station acknowledges the failure of "the regular amplifier by throwing the switch I50 to the left thereby to open the contacts I53; so as to open the circuit to the audible alarm I I6; The operation of the switch to the left brings about the closing of contacts I54 which are connected to conductor I28 so that at each five minute-interval when the relay 240 isenergized potential is supplied from the negative ter minal of the exchange battery through resistor 245 and contacts 24I to conductor I28 which is connected through contacts I54 of switch I50 to the alarm I I6 which is connected through conductor I21 and contacts 23I of relay 230 to thepositive terminal of the regular exchange battery. Thus every five minutes the audible alarm I IE will be energized for 'a short interval to continue to warn the attendant that the regular amplifier has not yetbeen placed back in service; Periodic loudspeaker testing At greater time intervals, such as several hours, or, for example; four hours, the entire loudspeaking communication system is subjected to a' test.

The detent on the cam 829 actuates its switch at thesame time that the detent on the cam 835 actuates its switch. Therefore relays I40 and 150 are energized in succession and relay I60 is momentarily energized. Relay I60 brings about energization of relay BIO which starts the motor 831. The closing of the switch 834 by the cam 829 completes a circuit from the positive -terby'the actuating of switch AS504 whenever all of the stations of the system are to be connected to the loudspeaking amplifiers. The relay 620, it will be remembered, operatesto cause all of thestations to be connected to the amplifiers by the operation of the corresponding relays N250. Operation of the relay N250 places positive potential through the contacts 252 upon the conductor 238fso'that the line ground test apparatus, by preventing the operation of any N320 relay, is not permitted to disconnect any of the lines from the regular exchange battery. The relay N250 also closes contacts253 thereby placing a short circuit across the relay which, however, has no efiect since this relay was energized at thebeginning of the cycle of testing prior to the operation of the relays 620 and N250. The motor 831 through the gear box 838 'drives the cams 839, B43 and 846' ina manner as was previously described. This brings about energization of the tone generator 845 which transmits a series of tone impulses to the regular amplifier and then to thespare amplifier. When the motor 031 has completed a complete revolution of each of the cams,-each of the outlying stations is required .to acknowledge the receipt of the test impulses by actuating its impulsing'device 441. This prominal ofthe regular exchange battery through contacts MI and switch contacts83B, relay contacts 823, relaycontacts 8I2, to conductor 53'! whichisconncted to relay 620 and also to signal -lamp AS505. The signal lamp A S505 is the one which is illuminated either by the testing apparatusor by the attendantat the control station' acknowledgment fier 46!. the conductors 4H5, Whenever the alternating duces an acknowledgment at the control station in a manner previously'described, whereby the lamp N525 is illuminated. When all of the stations haveresponded by transniitting the acknowledgment impulses the attendant at the control st ationmay return to normal the signal lamps N525 by actuating the switch 5) to the left to break the contacts 5| I, which thereupon will bring about the release of each of therelays corresponding to N1).

Auxiliary power sources The control station and each outlying station is provided with a connection to a regular power source and is provided with an auxiliary source of power. At the control station this power supply has been designated by the rectangle 8I0 and this power supplies energy to g the motor 821, to the amplifiersZilI and $20!,

and to other equipment such as the anode power supply in the event that the tone generator 845 utilizes vacuum tubes or a vacuum tube ampiifier. In order to simplify the disclosure in the presentinstance, the auxiliary and commercial power supply sources haveonly been shown at the outlying station N400. An alternating current source is provided for the conductors 4I6 which are connected toan alternating current re1ayv420 which completes a circuit through'contacts 42I and 423 to the ampli- A relay 4H1 is also connected across current source connected to the conductors M8 fails or is interrupted, the relays 4I0and 420 are deenergized whereby a storage battery or auxiliary power source 454 is arranged to supply energy to the amplifier 46L The relay 4H3 when deenergized breaks contacts 4| I and closes contacts4I2 thereby connecting the battery M4 to an inverter 42'i,the output of which is now connected through relay contacts 422 and 424 to the amplifier 26!. Across the outputin the inverter 42] there is connected a signal lamp 428 to visually indicate that' the inverter and auxiliary power source are in operation. The

completion of the contact M2 of the relay4I0 also connects through contacts 4I9 an audible signal device 4I'I across the battery 4I4, thereby 

